Initial Setup

First things first, here's a guide to get you set up on installing Ubuntu to your Switch:

https://gbatemp.net/threads/l4t-ubuntu-a-fully-featured-linux-on-your-switch.537301/

After you've got it set up, open a terminal (Ctrl + Alt + T or open Terminal from the app list), then copy and paste the following command to automatically update, then run the megascript: (hint: if running over ssh with no display, remove "gui")

sudo apt update && sudo apt upgrade -y && sudo apt install bash dialog gnutls-bin curl zenity -y && hash -r && bash <( curl https://raw.githubusercontent.com/cobalt2727/L4T-Megascript/master/core_refactor.sh ) "gui"

An application "L4T Megascript" will be added to your system after you run the megascript for the first time.

IMPORTANT NOTE IF YOU GET ERRORS INVOLVING TURUL REPOSITORIES

You haven't finished fully installing L4T Ubuntu, apply whatever the latest update is on top of 3.2.0. A guide can be found here:
L4T Ubuntu GBATemp project page

We HIGHLY recommend that you first run the initial setup script to ensure everything is in working order.
Here's all the options included in that:

Flatpack Fix

Workaround permissions issues due to options not supported in L4T Kernel

JoyCon Mouse

Lets you use the joycons as - you guessed it - a mouse/keyboard.
Note: JoyCons, Switch Pro Controller, Dualshock 4 (wired only), XBox One Controller (wireless only), and Nintendo GameCube Controllers (when using the ToadKing Gamecube Driver) are supported.

Default button configs for JoyCons/Pro Controller (other controllers similar):

Button	Key
B	Left Click
A	Right Click
X	Middle Mouse Button
L	Volume Down
R	Volume Up
ZR	Brightness Up
ZL	Brightness Down
D-PAD	Keyboard Arrow Keys
Screenshot	Turn the mouse off and on (leave off when playing games)
Home	Escape
+	Enter
-	Back
Right Stick Click	F5
Left Stick XY	Mouse XY
Right Stick XY	Scroll XY

SDL2

Builds and installs newer patched SDL2. It's a requirement for many games in the script, but can take some time to set up.

The following programs require SDL2:

SRB2, SRB2Kart, CSE2-Tweaks, SuperTux2, Celeste (Pico-8 Port), Flappy Bird, SM64 Port, RetroPie (automatically installs with Retropie)
List in progress

And that's all! You're all set to install any other program included in the megascript. Check the individual wiki pages to read more on a particular game or program.

(If possible, you definitely want to hook up a USB keyboard and mouse to make setup easier...)